Process for fabricating organic circuits

ABSTRACT

An organic semiconductor film is fabricated by applying a solution containing an organic semiconductor material and a solvent to a substrate, e.g., by solution casting, and evaporating the solvent. The characteristics of the substrate surface, the organic semiconductor material, and the process parameters are selected to provide desirable nucleation and crystal growth. The resultant organic semiconductor film contains a large area, e.g., a continuous area greater than 1 cm 2 , that exhibits a relatively high charge carrier mobility of at least about 10 −4  cm 2 V −1 s −1  room temperature.

This is a continuation divisional of application Ser. No. 09/280,172,filed on Mar. 29, 1999, now U.S. Pat No. 6,265,243.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to fabrication of organic circuits such ascircuits containing organic thin film transistors.

2. Discussion of the Related Art

Organic thin film transistors (TFTs) are expected to become keycomponents of the plastic circuitry in, among other things, displaydrivers of portable computers and pagers, and memory elements oftransaction cards and identification tags. A typical organic TFT isshown in FIG. 1. The TFT contains a source electrode 10, a drainelectrode 12, a gate electrode 14, a gate dielectric 16, a substrate 18,and the semiconductor material 20. When the TFT operates in anaccumulation mode, the charges injected from the source 10 into thesemiconductor are mobile and conduct the source-drain channel current,mainly in a thin channel region within about 100 Angstroms of thesemiconductor-dielectric interface. (See, e.g., M. A. Alam et al., “ATwo-Dimensional Simulation of Organic Transistors,” IEEE Transactions onElectron Devices, Vol. 44, No. 8 (1997).) In the configuration of FIG.1, the charge need only be injected laterally from the source 10 to formthe channel. In the absence of a gate field, the channel ideally has fewcharge carriers, and there is ideally no source-drain conduction. Theoff current is defined as the current flowing between the source 10 andthe drain 12 when charge has not been intentionally injected into thechannel by the application of a gate voltage, and for an accumulationmode TFT, this occurs for a gate-source voltage more positive (forp-channel) or negative (for n-channel) than a certain voltage known asthe threshold voltage. (See, e.g., S. M. Sze, SemiconductorDevices—Physics and Technology, John Wiley & Sons (1985).) The oncurrent is defined as the current flowing between the source 10 and thedrain 12 when the channel is conducting. For a p-channelaccumulation-mode TFT, this occurs at a gate-source voltage morenegative than the threshold voltage, and for an n-channel accumulationmode TFT, this occurs at gate-source voltage more positive than thethreshold voltage. It is desirable for this threshold voltage to bezero, or slightly positive, for n-channel operation. Switching betweenon and off is accomplished by the application and removal of an electricfield from the gate electrode 14 across the gate dielectric 16 to thesemiconductor-dielectric interface, effectively charging a capacitor.

One of the most significant factors in bringing such TFTs intocommercial use is the ability to deposit organic semiconductingmaterials on a substrate quickly and easily (i.e., inexpensively), ascompared to silicon technology, e.g., by reel-to-reel printingprocesses. Yet, in order to exhibit suitable electrical properties, theorganic materials need to be deposited as thin, uniform, crystallinefilms, which is a difficult task when using easy, inexpensive processes.(See, e.g., C. Cai et al., “Self Assembly in Ultrahigh Vacuum: Growth ofOrganic Thin Film with a Stable In-Plane Directional Order,” J. Am.Chem. Soc., Vol. 120, 8563 (1998).)

Thus, those in the art have sought to attain the necessary uniformityand order in an organic semiconductor film by the easiest possiblefabrication techniques. Cai et al., supra, use an organic molecular beamdeposition technique to attain an ordered film, but such a technique isnot feasible for large-scale fabrication of organic circuits. Othergroups have used a polytetrafluoroethylene layer as a template for anorganic semiconductor layer, but the organic material is deposited by avapor phase method which, again, is unsuitable for inexpensivecommercial-scale fabrication. (See, e.g., P. Damman et al., “Morphologyand NLO properties of thin films of organic compounds obtained byepitaxial growth,” Optical Materials, Vol. 9, 423 (1998); and P. Lang etal., “Spectroscopic Evidence for a Substrate Dependent Orientation ofSexithiophene Thin Films Deposited onto Oriented PTFE,” J. Phys. Chem.B, Vol. 101, 8204 (1997).)

As suggested in Cai et al., supra, liquid phase techniques are the mostdesirable for fabrication of organic TFTs, since they involve simplyproviding the organic material in solution, depositing the solution on asubstrate, and removing the solvent. Such liquid phase techniques havebeen somewhat successful for polymeric semiconductor materials, asreflected, for example in Z. Bao et al., “High-Performance PlasticTransistors Fabricated by Printing Techniques,” Chem. Mater., Vol. 9,1299 (1997); and H. Sirringhaus et al., “Integrated OptoelectronicDevices Based on Conjugated Polymers,” Science, Vol. 280 (1998).However, polymeric semiconductor materials tend to be highly sensitiveto the fabrication conditions, are difficult to purify to the extentrequired for high mobilities and on/off ratios, and exhibit substantialbatch-to-batch variability. Oligomeric materials and/or polymers ofrelatively low molecular weight, and other low molecular weightcompounds, tend to be less sensitive and are generally able to bepurified such that high, and less environmentally sensitive, mobilitiesand on/off ratios are possible. Thus, liquid phase techniques fordepositing low molecular weight compounds, such as oligomericsemiconductor materials and low molecular weight polymeric materials,are of particular interest.

For example, several groups have experimented with solution casting ofthiophene oligomer films, in which a solution of the organic material isessentially dropped onto a substrate, and the solvent is evaporated byheating. However, these processes have generally provided relativelypoor uniformity and coverage from such oligomeric solution casting.Relatively large areas, e.g., greater than 1 cm², exhibiting usefulsemiconductor properties have thus been difficult to attain. Moreimportantly, the obtained mobilities, even over small areas, have oftenbeen unacceptably low or non-uniform compared to films formed by vaporphase techniques. (See, e.g., A. Stabel and J. P. Rabe, “Scanningtunneling microscopy of alkylated oligothiophenes at interfaces withgraphite,” Synthetic Metals, Vol. 67, 47 (1994); H. E. Katz et al.,“Synthesis, Solubility, and Field-Effect Mobility of Elongated andOxa-substituted α,ω-Dialkyl Thiophene Oligomers. Extension of ‘PolarIntermediate’ Synthetic Strategy and Solution Deposition on TransistorSubstrates,” Chemistry of Materials, Vol. 10, No. 2, 633 (1998); and H.Akimichi et al., “Field-effect transistors using alkyl substitutedoligothiophenes,” Appl. Phys. Lett., Vol. 58, No. 14, 1500 (1991).)

Spin-coating of oligomeric solutions onto a substrate has been performedmore successfully, as reflected in C. D. Dimitrakopoulos et al.,“trans-trans-2,5-Bis-[2-{5-(2,2′-bithienyl)} ethenyl]thiophene:synthesis, characterization, thin film deposition and fabrication oforganic field-effect transistors,” Synthetic Metals, Vol. 89, 193(1997); and F. Garnier et al., “Dihexylquarterthiophene, ATwo-Dimensional Liquid Crystal-like Organic Semiconductor with HighTransport Properties,” Chem. Mater., Vol. 10, 3334 (1998). Spin-coatingis wasteful, however, in that much of the solution flies off thesubstrate. Also, the technique is incompatible with the desired printingfabrication processes for organic TFTs, e.g., reel-to-reel processes ona flexible substrate, and is therefore more of a laboratory techniquethan a potential commercial process.

Thus, improved methods are desired for forming organic semiconductorfilms from low molecular weight organic semiconductor compounds. Ofparticular interest are non-spinning techniques for depositing uniform,ordered organic films from solution.

SUMMARY OF THE INVENTION

In one aspect,the invention features a device that includes a substratehaving a flourinated surface and an organic semiconductor film that isdeposited on the substrate. The film includes a continuoius area greaterthan 1 cm² and exhibits a charge carrier moibility of at least about10⁻⁴ cm²V⁻¹s⁻¹ at room temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a typical organic thin film transistor.

DETAILED DESCRIPTION OF THE INVENTION

A liquid phase technique, advantageously a non-spinning technique suchas solution casting, is used to form a crystalline or polycrystallineorganic semiconductor film from a solution of a relatively low molecularweight, e.g., oligomeric, organic semiconducting compound. The resultantfilm exhibits, over a relatively large continuous area of at least 1cm^(2,) a desirable charge carrier mobility of at least about 10⁻⁴cm²V⁻s⁻¹, advantageously at least 5×10⁻³ cm²V⁻¹s⁻¹ at room temperature.The film advantageously also exhibits an on/off ratio of at least 5,advantgeously at least 100.

(As used herein, on/off ratio refers to the ratio of the source-draincurrents measured for at least one value of the gate voltage less than100 volts on, and a gate voltage of zero volts off, in air, on adielectric having a capacitance of about 10⁻⁸ F/cm² and a resistivity ofat least 10 ¹⁰ ohm-cm, for a device operated in the saturationregime,using the same drain voltage to measure both currents. Organicsemiconductor film indicates a continuous layer of organic material on asubstrate that exhibits, over at least a portion thereof, a chargecarrier mobility of at least about 10⁻⁴ cm²V⁻¹s⁻¹ at room temperature.Organic semiconductor compound, as used herein, indicates the molecularconstituent or constituents of an organic semiconductor film, where allsuch constituents have a molecular weight less than 1000.)

It has been found that there are several principles to apply in order tosuccessfully fabricate these organic semiconductor films from solutionsof low molecular weight organic semiconductor compounds. First,nucleation of crystallites should be substantially restricted to theinterface between the solution and the substrate, as opposed tonucleation within the solution. Second, it is desirable to induce soliddeposition from solution before the pool of solution unacceptablycontracts in area. Third, overly fast crystallite growth at the edges ofthe pool of solution, relative to depsition across the pool area, shouldbe avoided. Fourth, the film should have a substantially connectedmorphology rather than isolated crystallites. These principles providetwo-dimensional growth across the substrate and high uniformity andorder in the resultant films. In one embodiment, these principles aresubstantially met by using an elevated deposition temperature, a dilutesolution, and a substrate having a fluorinated surface. The elevatedtemperture and dilute solution reduce nucleation within the solution,while the fluorinated surface appears to promote nucleation over thesolution-substrate interface.

According to the invention, a crystalline or polycrystalline organicsemiconductor film is formed by a liquid phase technique from a solutionof a relatively low molecular weight, e.g., oligomeric, organicsemiconducting compound, advantageously from a non-spinning techniquesuch as solution casting. The process is performed by following fourbasic principles. First, nucleation of crystallites is substantiallyrestricted to the interface between the solution and the substrate, asopposed to nucleation within the solution. Second, solid deposition fromsolution begins before the pool of solution unacceptably contracts inarea. Third, materials and conditions that cause overly fast crystallitegrowth at the edges of the pool of solution are avoided. Fourth, thefilm should have a substantially connected morphology rather thanisolated crystallites. The invention applies these principles tosuccessfully fabricate high-quality organic semiconductor films from lowmolecular weight compounds.

To promote nucleation at the surface-solution interface, as opposed towithin the solution, several guidelines are followed. Depositionconditions of high supersaturation are advantageously avoided, such thatmassive nucleation is unlikely. Temperature is kept relatively high,solutions are kept dilute, and extremely insoluble materials (e.g., asolubility limit of <10 ppm at 100° C.) are avoided. In an exemplaryembodiment, the solution poorly wets the substrate surface, e.g., acontact angle of at least 50° (such as by use of a fluorinated surface,as discussed below). A high contact angle allows a large volume ofsolution to be placed onto a given surface area, making it possible todeposit enough solute from even a dilute solution.

Generally, contraction is also reduced or avoided when the contact angleis high. Specifically, a high contact angle ensures that the pool ofsolution will not become overly thin at its edges during evaporation.Such thin areas are unstable and tend to contract. However, in somecases, it may be possible to deposit a useful film according to theinvention with a low contact angle.

As mentioned above, it is advantageous to use solutes that tend to avoidsupersaturation before nucleating. This characteristic is able to betested by taking a sample of the solution and monitoring whether thesolute crystallizes gradually at the temperature or concentration ofdissolution or whether the concentration moves past saturationconditions well before crystallization occurs. The latter would suggestthat supersaturation occurs before deposition, which would lead to largedroplet shrinkage followed by sudden deposition of solid in a smallarea, neither of which is desirable for fabricating the organicsemiconductor films of the invention. Further, preferential wetting ofcrystallites by the solution, relative to the substrate surface, isdesirable because deposited crystallites would then tend to hold thepool of solution in place, thereby inhibiting shrinkage in area. Suchpreferential wetting would be expected if the contact angle of solutionon the deposited material is less than the contact angle of solution onthe substrate surface. Moreover, if the solution droplet becomes thinenough while still substantially maintaining its original area coverage,crystal growth would become confined to two-dimensional space, whichfavors a desirable morphology (in the case of such thinning, it may bepossible to obtain a useful film with a low contact angle).

Growth at the edge of a solution pool is determined by rates ofnucleation and of enlargement of the crystal nuclei. The variety offactors that influence such nucleation and enlargement have been studiedextensively, but the particular relationships have yet to be fullyunderstood. In the invention, however, it has been observed thatcompounds with more polar or quadrupolar aromatic or heteroaromatic ringsystems, such as bithiazole, appear to deposit from solutionpreferentially, and undesirably, at nuclei formed at a pool boundary,particularly at temperatures only slightly higher than ambient. Incontrast, less polar, thiophene systems do not appear to exhibit suchpreferential nucleation along a pool boundary. A simple test is usefulfor determining materials suitable for the invention which tend to avoidfast growth at the edge of a solution pool. Specifically, a drop ofsolution is placed onto a substrate and allowed to evaporate/deposit. Ifa pronounced ring or rings form, separated by or encirclingsubstantially empty regions, the material system is unlikely to promotethe desired uniform, two-dimensional growth, but will instead tend toform distinct aggregates of material.

The desired interconnected morphology is generally attained by meetingthe previously-discussed guidelines. In particular, two-dimensionalgrowth provided by avoidance of edge-preferential nucleation contributesto interconnectivity.

Any substrate/solution systems, using a solute of organic materialcapable of exhibiting semiconductor properties, meeting these principlesare expected to provide desirable properties, e.g., an organicsemiconductor film exhibiting, over a relatively large continuous areaof at least 1 cm², advantageously at least 2 cm², a desirable chargecarrier mobility of at least about 10⁻⁴ cm²V⁻¹s⁻¹, advantageously atleast 5×10⁻³ cm²V⁻¹s⁻¹ at room temperature. Advantageously, theuniformity of the continuous area is such that 80% of this continuousarea exhibits a charge carrier mobility within a factor of two of theaverage charge carrier mobility of the continuous area. This continuousarea advantageously also exhibits an on/off ratio of at least 5,advantageously at least 100.

Advantageously, a fluorinated organic surface is provided to promoteattainment of these principles, particularly when the semiconductorcompound is not fluorinated. As mentioned above, fluorination promotessuch attainment by decreasing the wettability of the substrate surface,particularly by a non-fluorinated solvent, thereby providing a highcontact angle (e.g., at least 50°). To provide the fluorinatedsubstrate, it is possible to treat the surface of a non-fluorinatedsubstrate with a fluorinated compound. Techniques for doing so includedipping the substrate into a reagent that effects the binding offluorinated groups such as fluoroalkyl chains to the substrate,evaporating such a reagent onto the substrate, or spinning onto asubstrate a material containing such groups. It is also possible forthese surface-treatment techniques to include removal of solvents orby-products of the binding step, e.g., by vaporization or rinsing.Instead of depositing a fluorinated material onto a substrate, it isalso possible to provide a fluorinated substrate material, e.g., adielectric polymeric material rich in fluoroalkyl chains.

The fluorine concentration on the substrate surface should be sufficientto alter the wetting properties of the substrate surface relative to thesolution. In particular, treatment of non-fluorinated substrates by afluorinated silane has been found to be advantageous, particularly wherethe fluorinated silane is partially oligomerized prior to application.The partial oligomerization is generally performed either by (a) areaction with sufficient water to cause a degree of oligomerization ofabout 1.2 to about 3 (leading to a product referred to as oligomerized),or (b) by partially gelling the silane, e.g., with aqueous HCl, andusing the xylene-soluble fraction of the resultant material (leading toa product referred to as partly gelled). (Useful fluorinated silanescontain a silicon atom having ≧1 leaving group attached thereto, and anorganic group not on the leaving group that provides sufficient CFgroups to change the contact angle of a solution by at least 10°.) Onesuch fluorinated silane is C₈F₁₇C₂H₄Si(OEt)₃. For fabrication of organiccircuits, the substrate is, or has a surface layer of, an insulatingmaterial, typically exhibiting an electrical resistivity of at least10¹⁰ ohm-cm. Insulating materials include, but are not limited to,silicon dioxide, polyimide, and polyvinylphenol.

A variety of low molecular weight organic semiconducting compounds(molecular weight less than 1000) capable of forming an organicsemiconducting film are suitable for use in the invention, provided theguidelines discussed herein are able to be met. Some useful compoundsare known in the art. Non-polar thiophene oligomers, which are p-typesemiconductors, appear to be particularly suitable for use. Specificp-type organic semiconductor compounds useful in the invention,particularly with a fluorinated substrate surface, includeα,ω-dihexyl-α-sexithiophene (DHα6T), α,ω-dihexyl-α-quinquethiophene(DHα5T), and α,ω-bis(3-butoxypropyl)-α6T.

It is also possible to use an n-type organic semiconductor. Inparticular, as discussed in co-filed, co-assigned application entitled“Device Comprising N-Channel Semiconductor Material” (our referenceKatz-Li-Lovinger 31-2-3) it is possible to form useful n-channel filmsfrom liquid phase deposition. Contemplated compounds include fused-ringtetracarboxylic diimides, including naphthalene 1,4,5,8 tetracarboxylicacid diimides, naphthalene 2,3,6,7 tetracarboxylic acid diimides,anthracene 2,3,6,7-tetracarboxylic acid diimides, and heterocyclicvariants thereof. One advantageous group of compounds is naphthalene1,4,5,8-tetracarboxylic acid diimides with linear chains of four totwelve saturated atoms, generally carbon atoms, affixed to each of thetwo imide nitrogens. Advantageously, at least a portion of thesubstituents on the carbons of the linear chains are fluorosubstituents, which appear to improve the capacity for operation in air.

A suitable solvent is selected based on the particular organicsemiconducting compound used, as well as the wetting, crystalnucleation, and crystal growth on the substrate surface. Many organicsemiconducting materials are relatively insoluble, with a solubilityrange in a solvent of about 10 to about 1,000 ppm. Moderately polararomatic solvents are generally used to ensure adequate solubility. (Amoderately polar aromatic solvent indicates a compound containing anaromatic or heteroaromatic ring, typically with alkyl and/or halogensubstituents.) Suitable solvents include, but are not limited to,toluene, chlorobenzene, 1,2,4-trichlorobenzene, and 3-methylthiophene.Useful solvents for the naphthalene or anthracene based-compoundsinclude moderately polar aromatic solvents containingtrifluoromethylphenyl groups.

The device of the invention is typically a circuit containing organicsemiconductor films, with such films optionally being the activematerials of one or more thin film transistors. (See, e.g., H. E. Katz,“Organic molecular solids as thin film transistor semiconductors,” J.Mater. Chem., Vol. 7, No. 3, 369 (1997); and H. E. Katz et al., “Oligo-and Polythiophene Field Effect Transistors,” Chapter 9, Handbook ofOligo- and Polythiophenes, D. Fichou, ed., Wiley-VCH (1999).) A processfor forming such a device involves providing at least one substrate,electrode material and/or dielectric material, and depositing one ormore organic semiconductor films onto the substrate, electrode, and/ordielectric. For ease of processing, it is possible to use a substrate ofa polymeric insulating material, such as a polyimide. One desirablefabrication process is a reel-to-reel process, in which a continuoussheet of substrate material is advanced in stages, with one or morematerials deposited, patterned, or modified at each stage, e.g., byprinting techniques. According to the invention, it would be possible toapply a film or pool of a solution containing one or more organicsemiconductor compounds, e.g., by dispensing through a valve, byspraying through a nozzle, or by a printing technique, and evaporatingthe solvent to leave an organic semiconductor film. It is possible toheat the substrate, or provide a vacuum before, during, or afterapplication of the solution. It is thereby possible to form an organicsemiconductor film without the need to separate the region of thesubstrate receiving the film from the rest of the sheet, such thatimproved process efficiency and lower cost are achieved.

Moreover, using both p-channel and n-channel organic semiconductormaterials, it is possible, according to the invention, to fabricate acomplementary circuit by liquid phase deposition. (See, e.g., A.Dodabalapur et al., “Complementary circuits with organic transistors,”Appl. Phys. Lett., Vol. 69, No. 27, 4227 (1996).) In particular, simplecomponents such as inverters have been realized using complementarycircuit architecture. Advantages of complementary circuits, relative toordinary TFT circuits, include lower power dissipation, longer lifetime,and better tolerance of noise.

The invention will be further clarified by the following examples, whichare intended to be exemplary.

EXAMPLES 1 AND 2

Procedure:

Semiconductor compounds used were fabricated according to standardtechniques. Chlorobenzene and 1,2,4-trichlorobenzene were washed withconcentrated sulfuric acid and aqueous sodium carbonate and distilledfrom P₂O₅. Other solvents were the purest available commercial grades.

Substrates were: silicon dioxide (heavily phosphorus-doped (n-type)silicon with 3000 Å of thermal oxide thereon); Amoco polyimide (indiumtin oxide glass coated with about 1 to 2 μm of Amoco Ultradel™photocurable polyimide, spun from 8% w/v γ-butyrolacetone solution at1200 rpm, baked for about 1 hour at 130° C., and UV-cured for about 30minutes); JSR polyimide (about 1 to 2 μm of JSR Optimer™ AL3046polyimide, spun from 8% w/v γ-butyrolacetone solution at 1400 rpm, bakedfor about 1 hour at 120° C.); or polyvinylphenol on SiO₂/Si substrates(about 1 to 2 μm of Aldrich polyvinylphenol with an average molecularweight of ca. 20,000, spun from an 8% w/v acetone solution at 1200 rpm).

Fluorinated surfaces were: fluorinated silane, either partly gelled oroligomerized, the silane deposited by immersing substrates in 1%C₈F₁₇C₂H₄Si(OEt)₃ reagent solution in xylene at 80° C. for 10 minutes,followed by rinsing with toluene (oligomerized silane was partiallyhydrolyzed by heating with a 5% solution of 1.2N HCl in ethanol(containing 0.25 to 0.5 equiv of water), adding 10 volumes of toluene,and reheating to boil out the ethanol); or fluoroacrylate (provided byspin-coating an overlayer of 3M Fluoroacrylate Coating 722, 2% solutionin volatile fluorinated at 1200 rpm).

Semiconductor films were applied by transferring 0.1 to 0.3 mL ofpreheated solution with a heated pipette onto substrates that had beenthermally equilibrated in a vacuum oven, at temperatures noted below andat atmospheric pressure. A vacuum of about 0.2 atm was pulled for 1 to 2hours—until the solvent was removed. Gold electrodes were deposited byevaporation through shadow masks. Carbon electrodes were painted from anisopropanol suspension using a paintbrush. Characterization wasperformed by conventional techniques.

Example 1

DHα6T was deposited onto both untreated and fluorinated substrates fromchlorobenzene at 60° C.±10° C. For these samples, Table I presents theconcentration of the DHα6T in solution, the substrate, the surfacecoating (if any), the mobility, and the surface area over which themobility was exhibited.

TABLE I Area Concen- exhibiting tration Surface Mobility mobility (ppm)Substrate Coating (cm²/V-sec) (cm²) 30 Amoco PI — 0.005-0.1  <0.2 50Amoco PI — ˜0.001 <0.2 25 Amoco PI 3M 722 0.05 2-3 50 Amoco PIFluorinated Silane 0.003-0.005 >1 (partly gelled) 50 Amoco PIFluorinated Silane 0.06-0.08 >1 (oligomerized) 50 Amoco PIOctadecyltrimethoxy — <0.2 silane (non-fluorinated) 60 SiO₂/Si — 0.1<0.2 75 Amoco P1 Fluorinated Silane 0.03 2 (oligomerized)

Example 2

DHα5T was deposited onto both untreated and fluorinated substrates fromseveral solutions at a concentration of 400 ppm at 60 to 70° C. For thesamples, Table II presents the particular solvent, the substrate, thesurface coating (if any), the mobility, and the area over which themobility was exhibited.

TABLE II Area exhibiting Surface Mobility mobility Solvent SubstrateCoating (cm²/V-sec) (cm²) Toluene SiO₂/Si — ≦0.17  >1^(a) TolueneSiO₂/Si Fluorinated Silane 0.05-0.06 >1^(b) (oligomerized) Chloro-SiO₂/Si — ≦0.02  >1^(a) benzene Chloro- SiO₂/Si Fluorinated Silane0.03-0.04 >1^(b) benzene (oligomerized) Toluene JSR PI/SiO₂/Si — ≦0.03  0.5^(a) Toluene JSR PI/SiO₂/Si Fluorinated Silane 0.04 >1^(b)(oligomerized) Toluene Polyvinyiphenol/ — 0.07  0.5^(a) SiO₂/Si ToluenePolyvinylphenol/ Fluorinated Silane 0.06 >1^(b) SiO₂/Si (oligomerized)Chloro- SiO₂/Si 3M 722 0.03-0.04  1^(b) benzene ^(a)Uneven coverage:some mobilities measured in the film were up to 10× different from thismobility value. ^(b)Even coverage: mobilities measured in variousregions of the film were all within a factor of 2 of this mobilityvalue.

Example 3

A solution ofN,N′-bis(1H,1H-perfluorooctyl)naphthalene-1,4,5,8-tetracarboxylicdiimide, 400 parts per million by weight, in α,α,α-trifluorotoluene, wasprepared by gentle heating. This solution was cast onto a silicon/SiO₂substrate that had been preheated to about 100° C. The solventevaporated within about 2 minutes. A 1 cm² region of the substratebecame coated with a thin deposit that showed significant n-channelactivity when tested with gold electrodes. The highest mobility obtainedwas 0.07 cm²/Vs measured in air with a device width/length ratio of 1.7,although other parts of the area showed mobility an order of magnitudelower.

An uncoated region of the substrate was used to cast a film of DHα5Tfrom a 400 ppm toluene solution at 100° C. under vacuum. Gold electrodeswere deposited on the thienyl compound. Inverter circuits wereconstructed by connecting the drain electrode of a diimide device withthe drain electrode of a thienyl device, and forming an output contactfrom the connection. The effective W/L ratio of the thienyl deviceranged from 1.7 to 0.1. The output was switched between ±0-10 volts and±68-98 volts by sweeping the gate over a range of 60 volts and applyinga voltage of 100 volts to the source of the thienyl device, or −100volts to the source of the diimide device. Output voltage differentialsas high as 95 volts and gains as high as 10 were observed.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein.

What is claimed is:
 1. A device comprising: a substrate comprising afluorinated surface; and an organic semiconductor film deposited on thesubstrate, the film formed from a organic semiconductor compound,wherein the film comprises a continuous area greater than 1 cm² thatexhibits a charge carrier mobility of at least about 10⁻⁴ cm²V⁻¹s⁻¹ atroom temperature.
 2. The device of claim 1, wherein the continuous areaexhibits an on/off ratio of at least
 5. 3. The device of claim 1,wherein the continuous area greater than 1 cm² exhibits a charge carriermobility of at least about 5×10⁻³ cm²V⁻¹s⁻¹ at room temperature.
 4. Thedevice of claim 1, wherein the fluorinated surface comprises afluorinated silane.
 5. The device of claim 4, wherein the substratefurther comprises a polymeric material underlying the fluorinatedsurface.
 6. The device of claim 1, wherein the organic semiconductorcompound is selected from α,ω-dihexyl-α-sexithiophene,α,ω-dihexyl-α-quinquethiophene, α,ω-bis(3-butoxypropyl)-α-sexithiophene,and naphthalene 1,4,5,8 tetracarboxylic acid diimides.
 7. The device ofclaim 1, wherein the film comprises a continuous area greater than 2 cm²that exhibits a charge carrier mobility of at least about 10⁻⁴ cm²V⁻¹s⁻¹at room temperature.
 8. The device of claim 1, wherein 80% of thecontinuous area exhibits a charge carrier mobility within a factor oftwo of the average charge carrier mobility of the continuous area.